3D imaging and anisotropy mapping of the lamb disc for biomechanical and regenerative insights

The temporomandibular joint (TMJ) relies on a fibrocartilaginous disc for stabilization and load distribution. When the disc degenerates, current replacement options fail to restore native biomechanics. Developing effective implants requires detailed knowledge of the disc's structure. The present work provides a full-volume, three-dimensional characterization of collagen fiber architecture and anisotropy in a large animal model with anatomical and functional similarities to the human joint.

A multimodal 3D imaging workflow was implemented, combining cone-beam CT for anatomical context and synchrotron phase-contrast micro-CT for high-resolution visualization of the ovine temporomandibular joint disc, cartilage, ligament, and subchondral bone. Deep-learning segmentation enabled full-volume tissue segmentation. Fiber orientation and anisotropy were quantified using mean intercept length (Mean Intercept Length)-derived eigenvector fields, with analysis performed across anatomical axes and planes. Histological sections validated fiber segmentation and regional differences in extracellular matrix organization.

The lamb TMJ disc displayed a heterogeneous but highly ordered collagen network. Strong lateromedial alignment formed frontal-plane reinforcement bands, while a craniocaudal tensile corridor dominated the sagittal plane, and mixed lateromedial-ventrodorsal orientations characterized the transverse plane. Anisotropy was highest in the peripheral rims and lower in the central zone, reflecting a functional division between stabilization and deformation. Quantitative analysis demonstrated an orthotropic organization, with distinct dominant fiber populations aligned along the lateral-medial, ventral-dorsal, and cranial-caudal axes. Subchondral bone beneath the disc exhibited a fine, highly anisotropic trabecular lattice with reduced spacing, complementing the disc's structural organization.

This study provides the first full-volume, plane-resolved 3D description of collagen anisotropy in the ovine TMJ disc. The orthotropic fiber architecture and regional anisotropy gradients identified here clarify direction-dependent mechanical behavior and offer quantitative benchmarks for the design of biomimetic scaffolds and regenerative TMJ disc replacements.